Electronic musical instrument diode keying with isolation and wave-shaping

ABSTRACT

An electronic musical instrument, such as an organ, utilizing a plurality of constantly operating square wave generators, with the generators connected to utilization circuits by means of diodes which are normally biased off. Potential is switched selectively to the diodes upon closure of key switches to play the various tones. Diodes are shared in order that two diodes might be in series between each tone generator and utilization circuit for maximum isolation, while conserving the total number of diodes necessary. The diodes are supplied with potential through circuits which serve as integrating circuits for the square waves, whereby to round off the attack to produce or lead toward sawtooth wave shapes. Groups of diodes also are provided with are switched on simultaneously, and are connected to previously mentioned diodes for playing preselected groups of notes simultaneously to simulate a chimes effect.

United States Patent Harold O. Schwartz;

William V. Machanian; Robert D. Barry; Richard E. Barbas, North Tonawanda, N.Y. 455,233

May 12, 1965 Mar. 9, 1971 The Wurlitzer Company Chicago, Ill.

lnventors Appl. No. Filed Patented Assignee ELECTRONIC MUSICAL INSTRUMENT DIODE KEYIN G WITH ISOLATION AND WAVE-SHAPING 31 Claims, 6 Drawing Figs.

US. Cl 84/l.01, 84/1.17, 84/l.l9, 84/124, 84/126 Int. Cl G10h l/02, GlOh 5/10 Field ol'Seareh 84/10],

Primary Examiner-W. E. Ray Att0rney- Olson, Trexler, Wolters & Bushnell ABSTRACT: An electronic musical instrument, such as an organ, utilizing a plurality of constantly operating square wave generators, with the generators connected to utilization circuits by means of diodes which are normally biased ofi. Potential is switched selectively to the diodes upon closure of key switches to play the various tones. Diodes are shared in order that two diodes might be in series between each tone generator and utilization circuit for maximum isolation, while conserving the total number of diodes necessary. The diodes are supplied with potential through circuits which serve as integrating circuits for the square waves, whereby to round off the attack to produce or lead toward sawtooth wave shapes. Groups of diodes also are provided which are switched on simultaneously, and are connected to the previously mentioned diodes for playing preselected groups of notes simultaneously to simulate a chimes effect.

PATENTED HAR 9:97: 5. 4

SHEET UF 2 PATENTEUMAR sum I 3,569,604

SHEET 2 OF 2 56 FILTERS %424452 m. 64

WLFarE/P:

ae-v94 95 116 W; FILTERS 16-1 v QZMMql/MW ELECTRQNTC MUSICAL INSTRUMENT DIODE KEYING WITH-ll HSOILATION AND WAVE-SHAPING This invention relates generally to the art of electronic musical instruments, and more particularly to improved key switching in electronic organs.

Although it has sometimes been done, it is undesirable in electronic musical instruments to have the key switches actually carry the signal. Not only does this limit versatility, but possible noise through corroded or dirty contacts in injected directly into the musical signal. Accordingly, in the present invention it is proposed to use key switches only for switching controlling potentials. The key-switched potentials are used for controlling the conduction of diodes which carry the signals. Diodes which are available commercially at reasonable prices do not have an infinite back resistance. Hence, a single diode inserted in series with the musical signal and normally biased off may transmit a small amount of signal. If other notes are being played, this is of little consequence, since the played notes mask the undesired signal. However, during periods of quiet any such signal pass can be most distracting. it is known that two diodes in series will add together their back resistances. However, if this is done with every tone generator in an electronic musical instrument, the expense becomes quite high.

Therefore, in accordance with the principles of the present invention, it is proposed to use diode switching in an electronic musical instrument in which some of the diodes are shared, while maintaining a series diode relationship, thereby materially reducing the cost and providing a high degree of signal isolation.

Broadly speaking, the primary object of the present invention is to provide an improved switchingsystem for electronic musical instruments.

It is another object of the present invention to provide an electronic musical instrument with certain special effects in switching.

it is a further object of the present invention to provide a switching system in an electronic musical instrument which is readily provided with a chimes effect.

Yet another object of the present invention is to.provide a switching system in an electronic musical instrument wherein the wave shape passed varies over the gamut of the instrument, thereby providing a type of formant filter common to conventional musical instruments.

Other and further objects and advantages of the present invention will be apparent from the following description when taken in connection with the accompanying drawings wherein:

FIG. I is a perspective view of an electronic organ constructed in accordance with the principles of the present invention;

FIG. 2 is a schematic wiring diagram of the switching circuits of the present invention;

FIGS. 30, 3b and 30 show different wave shapes as switched by the switching system;

FllG. 4 is a circuit functionally somewhat similar to FIG. 2 and forming a modification thereof.

Referring now in greater particularity to the FIGS. and first to MG. 1, there is shown generally an electronic organ l having a case 112 with an upstanding music rack 14. The organ is provided with an upper manual or keyboard 16 and a lower manual or keyboard 18. Various stop tablets 20 are provided in accordance with conventional practice. There is also provided a pedal clavier 22, and a swell pedal 24 for controlling the overall volume. The case contains various filters and amplifiers more or less in accordance with conventional practice, and loudspeakers are mounted behind a grill 26 at the front of the organ.

Turning now to FIG. 2, at the upper left corner thereof there is schematically illustrated a plurality of tone generators 28. There is at least one generator for each note of the organ, and for purposes of distinction, the first generator is labeled as 28-3, the second as 28-2, etc. down to 28-n, depending on the number of notes in the organ. The tone generators may be of any known or conventional type, and in the particular example comprise transistor oscillators. A square wave output is produced. The oscillators in accordance with conventional practice may comprise a series of master oscillators, one for each note of the upper octave, with a plurality of divider or slave oscillators. Each oscillator is grounded at one side, as indicated, and is connected through a resistor 30, there again being provided suffixes to distinguish the various circuits or notes from one another, to a first or common diode 32. It is believed that the skilled in the art will have no difficulty in understanding the duplication or multiplication of parts hereinafter, and hence only one note circuit is specifically shown, as a showing of more would hopelessly confuse the drawings. The first diode 32 comprises a common diode, as will be set forth with greater particularity hereinafter, and it is biased to conduct from right to left, considering the conventional current flow. Each of the generators 28 produces only a positive voltage, ranging from 1-14 volts in one particular organ, and from 1-18 or 20 volts in another particular organ. The bottom portion of each :square wave is not allowed to go to zero or below, but it maintained at a positive voltage, such as one volt.

The right side of the diode 32 is connected to a junction 34, and this junction is connected to a junction 36 grounded through a capacitor 38. The junction 36 is also connected to a second diode 40, also biased to conduct from right to left, and this diode is connected to a junction 42 which is grounded through a capacitor 44. The junction 42 is connected to a junction 44 which is connected to a resistor 45 leading to a sliding tap 46 on a potentiometer resistor 48. The tap is shunted to ground by a capacitor 47 of large value to ground out any AC appearing thereon. The potentiometer resistor is connected across a voltage source 50, conventionally shown as a battery, and having the top'end thereof at a negative potential, and the bottom end at a positive potential. The bottom end is grounded as shown. The tap 46 is common to all notes on the upper manual, and there is a resistor 45 for each note.

The junction 44 further is connected to a junction 52 which is grounded through a diode 54. The diode is biased to conduct in an upward direction i.e., from ground toward the junction 52.

The junction 52 further is connected to a junction 56, and this is connectedthrough a capacitor 58 to a junction 60. The junction 60 is connected through a resistor 62 to an output line 64 leading to one or more filters. The junction 60 further is connected through a similar resistor 66 to another output line 68 leading to different filters. There can be still further resistors, output lines and filters, as will be apparent. Connection also is made to the output line 64 through additional ones of the resistors-62, these again being provided with the suffixes as 62-1, 62-2, etc. to 62-n, whereby the output of additional ones of the generators 28-1 through .28-n, after having been switched by circuits duplicative of those be considered, are connected to the output filters. Similarly, connections are made from the same notes to the filters on the output line 68 through additional ones of the resistors 66, similar numerals from 66-1 through 66-n,again being used.

Returning to the junction 56, this junction is connected through a resistor 70 to a junction 72, the latter being connected to ground through a capacitor 74, and also connected through a resistor 76 to a junction 78. The junction 78 is grounded through a capacitor 80 and is directly connected to a junction 82. The junction 82 is connected through a resistor 84 to a junction 86. The junction 82 also is connected to .a junction 88, and this is connected through a capacitor to junction 86, the resistor 84 and capacitor 90 thereby being in parallel. The junction 86 is connected to a normally open sustain switch 92, the opposite side which is grounded.

The junction 88 is connected through a resistor 94 to a key switch 96, the opposite side of which is connected to a positive direct current supply line, nominally at +1 80 volts. As will be understood, there is a series of such key switches, labeled 96-1 through 96-n, one for each tone generator, and these are respectably connected through the additional ones of the resistors 94, specifically labeled 94-1 through 94-2. As will be understood, the circuit between the resistors 30 and the junction 60 and 88 are duplicated, there being one such circuit for each note.

The junction 34 is connected by means such as a wire 100 to a diode 102. Like the previous diodes, this diode is connected to conduct from right to left in the conventional sense. The diode is connected to a junction 104, and this is connected to ground through a capacitor 106. The junction is connected to a junction 108, and to another junction 110. Reference will be made to the junction 108 hereinafter, but reference now is made to the junction 110 which is connected through a capacitor 112 to a junction 114, and this is connected through a resistor 116 to an output line 118 leading to one or more wave-shaping filters. It is to be understood that the resistor 116 is duplicated in the same manner as parts heretofore described, being labeled as 116-1 through 116-n, comprising a very close analogy to the resistors 62 at the top of the FIG. There are also additional resistors 120, comprising resistors 120-1 through 120-n leading to another output line 122 connected to one or more filters.

Returning to the junction 110, the junction is also connected through a resistor 124 to a junction 126 which is grounded through a capacitor 128. The junction 126 is connected through a resistor 130 to a junction 132, and this is grounded through a capacitor 134. The junction 1-32 is directly connected to additional junctions 136 and 138, respectively connected through resistor 140 and capacitor 142 to a common junction 144, the resistor and capacitor thereby being in parallel. The junction 144 is connected to a normally open sustain switch 146, the opposite side of which is grounded. Connection is made from the junction 138 through a resistor 148 to a switch 150, the opposite side of which is connected to a positive supply line 152, indicated as +180 volts. As will be understood from what has gone before, there is a plurality of the resistors 148, respectively indicated as 148-1 through n, these respectively being connected through additional ones of the switches 150, indicated as 150-1 through 150-n all being connected to the positive supply line 152.

The switches 92 and 146 have heretofore been identified as sustain switches. The switches 96 and 150 are key switches. The switches 96 are respectively controlled by the keys of the upper manual 16, while the switches 150 are respectively controlled by the keys of the lower manual 18.

A further connection is made to the circuit for the playing of chimes. Thus, returning to the junction 108, connection is made to this junction through a resistor 154, the latter being connected to a diode 156 biased to conduct from left to right, as shown in the drawing. This diode is connected to a collector line 158, and the collector line is connected to a shunting resistor 160 and capacitor 162 combination, the two elements being in parallel and grounded, and to a key switch 150-x. This comprises an extra contact on one of the key switches 150 of the lower manual, and it is to be understood that the switch 150-x is duplicated. Specifically, about two octaves of chime key switches 150-x are provided. Connection is made from the switch 150-x through a resistor 164 to a positive potential supply 166 indicated as +21 volts.

The collector line 158 is connected through three more diodes 168, 170 and 172, respectively to resistors 174, 176, and 178 and thence to additional ones of the tone generators 28. The connection is each instance is indicated as being through a broken line, since it is not a direct connection, but goes perhaps through other circuits.

By way of specific example, if the note for which the complete circuit is shown be considered to be an E note, as indicated in parenthesis just to the right of the resistor 154, then the other three generators comprise G, C, and C an octave away, all as indicated directly adjacent the generators. The combination of the four notes produces a chimes tone.

Before continuing with further parts descriptions it is thought necessary to describe the operation of the circuit just set forth.

OPERATION Each of the tone generators 28 at all times puts forth an output, and for purposes of this disclosure it is 'to be borne in mind that this is square wave output. Further, it must be recalled that the voltage is always above zero. Thus, the diodes 32 and 40 operate in series to block the output from the corresponding tone generator 28 to the utilization circuits, comprising the output lines 64 and 68. Furthermore, the diodes 32 and 102 operate in a series to block the output of the generator 28 from the utilization circuits comprising the output lines 118 and 122. Thus, we have effectively four diodes, i.e., two pairs in series, with use of only three diodes. Hence, there is a 25 percent savings in diodes. Supposing it is desired to place an output on the output lines 118 and 122. One of the switches 150 under control of the lower manual keys is closed by depression of the corresponding key. Let us consider the switch 150-1 since it is the one for which the complete circuit is shown. 180 volts is passed by this switch, and this positive 180 volts biases on the diodes 102 and 32, whereby the output from the generator 28-1 passes over the resistor 30, through the diode 32, over the line and through the diode 102, and through the capacitor 112 and resistors 116 and to the output line 118 and 122.

it will be apparent that output is supplied to the lines 64 and 68 in the same manner by closing one of the switches 96, for example the switch 96-1, whereby to turn on the diodes 32 and 40 in series. It will be appreciated that the filters to which the lines 64 and 68 lead have individual stop tablets for turning on the filters and associated circuits, whereby either or both may be played simultaneously. The same is true in connection with the filters to which the lines 118 and 122 lead. By way of illustration, each of the upper output lines 64 and 118 may lead to filters providing a complex output, while the lines 68 and 122 may lead to flute filters for producing an output which is primarily fundamental with little or no harmonic.

Mention of operation has been made without reference to the sustain feature. With the sustain off, the capacitor 134 provides an initially greater current than there would be otherwise. This provides or cooperates to provide a pulse for triggering other circuits, such as for example the percussion circuits disclosed and claimed in H. O. Schwartz and Peter E. Maher, application U.S. Ser. No. 454,134, filed May 7, 1965, and entitled Post Signal Modulation for Electronic Musical lnstrument, now U.S. Pat. No. 3,365,993, dated Jan. 30, 1968.

The capacitor 128 helps to shape the attacked characteristic, whether or not the sustain is on. The capacitor 128 also contributes to the decay, the path being through the resistor 124.

With the sustain switch 146 closed, when key switch 150-1 is first closed, the capacitor 142 charges up. Positive v potential on this capacitor acts to hold open the diodes 102 and 32 for a predetermined time after the switch contact 150-1 is opened as the capacitor 142 discharges through thediodes, and also through the resistor 140. The importance of the resistor will be appreciated when it is considered that the sustain switch 146 might be opened during the playing of the note with the capacitor 142 charged. If it were not for the re sistor 140, of quite high value, the capacitor 142 would remain charged, and the note in question would start playing again upon closure of the switch 146 even though the note switch was not closed. The resistor 140 provides for discharge of the capacitor 142 in a second or so.

The sustain for the upper manual is in part the same as for the lower manual. That is, closing of the switch 92 causes the capacitor 90 to charge and discharge in basically the same manner as the capacitor 142 charges and discharges. However, a variable sustain is provided by the potentiometer 46 and 48. When the tap 46 is at the bottom of the resistor 48,

there is no effect. However, as the tap is moved up the resistor, a progressively greater negative voltage is applied at the junction 44. This turns on the diode 54 and provides an additional discharge path for the sustain capacitor 90. As will be appreciated, the length of the sustain is continuously variable by moving the tap 46 to different selected positions along the potentiometer resistor 48.

Operation of the chimes is very similar to that of playing a single note. When the key switch l50-x is closed, a positive potential is applied to the left side of the diode 156, thus turning on the diode 156 and also the diodes 168, 170 and 172. The potential passed by the diode 156 turns on the diodes 102 and 32. Similarly, the potential passed by the diodes 1 68, 170 and 172 turns on the two switching diodes of the other three selected generators 28. It will be appreciated that the resistors 154, 174', 176 and 178 are of low value, whereby the positive 21 volts is adequate to turn on the diodes. The contact 150-x is closed at the same time the contact 150-1 and a note and the chimes effect can be played simultaneously. Alternatively, the 180 volts can be switched off when it is desired to play the chimes without the accompanying note. Accordingly, simultaneously an output is applied from four properly related generators to produce a chime tone.

Whenever two of the series connected diodes are turned on, for example, the diodes 32 and 40, there is only one diode such as 102 blocking the signal from passage another utilization circuit. Of course there will be more leakage through this one diode thanthrough the two in the'series. However, this is insignificant since there is a signal passed to a utilization circuit through the diodes 32 and 40 which completely masks any leakage signal through the diode 102.

The switching circuits just described also produce a formant type of wave shaping. Thus, considering FIG. 3a, the input square wave is indicated at 180, and the particular wave in FIG. 3a is of a rather low frequency. There is a certain amount of rounding off of the attack (as indicated by the broken line at 182) in the switching circuit, due to the high impedance charging path through the resistors 76 and 70 to capacitors 74, 44 and 38, for example. In a low frequency signal the rounding off at 182 is relatively insignificant and the total wave passed, which comprises the broken line 182 and remaining solid lines to the right thereof, is essentially a square wave.

However, in FIG. 3b where a much'higher frequency, relatively toward the top of the keyboard is shown, the rounding off indicated by the broken line 182 may comprise the whole width or half cycle of the square wave 180. As a result, the output wave is a saw tooth wave rather than a square wave. An intermediate condition is shown in FIG. 30 wherein the rounded off attack portion 182 comprises an appreciable portion of the square wave 180. Part of the rounding off also is caused by the capacitor 58 which is provided primarily to decouple direct current from the output. Variations in resistors and capacitors can be used to determine the degree of the rounding off 182, as may be desired. However, in any event, it may be seen that the rounding off becomes progressively more important with higher frequencies changing from essentially a square wave to essentially a saw tooth. As is known, the square wave has only fundamental and odd harmonics. The saw tooth has the fundamental and all harmonics, while the combined wave has the fundamental and all harmonics, but emphasizes the odd harmonics. This produces a particularly desirable type of formant action leading to a distinct tone quality in the organ constructed in accordance with the principles of the present invention.

MODIFICATION A modification of the switching circuit is shown in FIG. 4. The switching circuit in FIG. 4 is shown for only one note, but it will be understood that other notes are incorporated in the same manner as in FIG. 2. Also, for purposes of simplicity, the chimes effect has been left off FIG. 4. It can be incorporated in exactly the same manner as FIG. 2. Many of the parts in FIG. 4 are the same as in FIG. 2, and to obviate the necessity of repetitious discussion, such parts are identified by like numerals with the addition of the suffix a.

More specifically, the tone generator 28a, again a square wave generator, is connected direct to the diode 32a, and the right side of the diode is shunted to ground through the capacitor 38a, as well as being connected to junction 36a. Junction 36a is connected to a junction 182 which, in turn, is connected to a resistor 184 leading to the diode 40a, shunted to ground by the capacitor 44a. The diode 40a is also connected to the junctions 42a and 44a and through the DC blocking capacitor 58a to junction 60a and to output resistors 62a and 66a respectively leading to output or collector lines 64a and 68a going on to suitable filters. t

The junction 44a also is connected through the resistor 70a to a junction 440 which leads through a resistor 45a to a variable sustain common switch movable contact 186. The mova ble contact may be engaged with a grounded fixed contact 188 for sustain off, or it may be moved up into engagement with a fixed contact 190 which is connected to a sliding tap 192 on a potentiometer resistor 194 having a negative voltage connected across it as indicated by a battery 196. The bottom end of the resistor 194 and the positive end of the battery 196 are grounded as shown.

The junction 440 also is connected to a junction 56a and a direct connected junction 56b. The junction 56:: is shunted to ground by a sustain capacitor a, and the junction 56b is shunted to ground through a diode 198, poled as shown to conduct in the conventional current sense from ground to the junction 56b.

The right side of the resistor 76a is connected to a junction 88a, and this is connected through a resistor 200 to a sustain diode 202, the latter being connected to a sustain common 204. It will be understood that most of the parts referred to heretofore are duplicated for different notes, but that the common 204 is common to all notes. There is single sustain switch 206, the other side of which is grounded or connected to a positive voltage.

From the junction 182 a resistor 208 leads to the diode l02a. The junction 104a on the right side of the diode is shunted to ground by a capacitor 106a. The junction 1080 is connected through DC blocking capacitor 112a to junction 114a, and hence to the resistors 116a and 120a and respectively to the output lines 118a and 122a.

The junction 108a is connected through the resistor 124a to junctions 136a and 138a, and these are shunted to ground through sustain capacitor 142a in parallel with resistor a. Resistor 130a leads to a junction 210 which in turn leads to resistor 148a and key switch 1500 to the input switching potential line 152a. It will be observed that the potential on lines 98a and 152a is plus 22 volts. The circuit of FIG. 4 has a lower input impedance than that of FIG. 2 and is suitable for use with lower voltages.

Finally, junction 210 is connected through a sustain resistor 212 to a sustain diode 214, and this leads to common 216 and sustain switch 146a. This is a two position switch, and for one position the switch is grounded, as shown, while in the other position with the sustain on, the switch is connected to a positive, relatively low voltage.

OPERATION OF MODIFICATION Operation of the circuit of FIG. 4 is quite similar to that of FIG. 2. If the switch 15011 is closed, for example, with the sustained off, then the positive potential is applied through the appropriate circuit elements to the diodes 102a and 32a in series, thereby to pass the signal to the output lines 1180 and 122a. The sustaincapacitor 142a charges rather quickly. It is a larger capacitor than in the circuit of FIG. 2 due to the lower voltage and lower impedances, and it is preferred that an electrolitic or tantalum capacitor be used. When the key switch 150a is allowed to reopen, the charge is quickly dissipated through resistor 130a, resistor 212 and diode 214 to the sustain common to ground.

On the other hand, if the sustain is on, the diode 214 will be above ground potential and the capacitor will be discharging to a higher potential than ground, whereby it will discharge more slowly. In fact, it cannot complete discharging through the diode 214.

The upper manual switching is similar to that just described. If the switch 96a is closed, a positive potential from the line 98a is applied through the appropriate circuits to turn on the diodes 40a and 32a whereby the signal passes to the output line 64a and 68a. If the sustain is off, the switch 206 is closed to ground. Hence, as soon as the key switch 96a is allowed to reopen, the sustain capacitor 90a quickly discharges through the resistors 76a and 200, and through the sustain diode 202.

If the variable sustain is used, a negative voltage is applied from the tap 192 through the switch 186 to the top of the diode 198 at 56b. This turns on the diode 198 to a greater or lesser extent to discharge the capacitor 904 at a rate depending on the extent of the negative voltage.

Those skilled in the art will doubtless be able to arrive at proper values for the circuit elements heretofore set forth. However, as a guide, suitable values are as follows, the letter capital R being used to aid in quick identification of the resistors, and capital C being used for capacitors:

R303.9K. ohms C44variable from one note to another R45-470K. ohms R70-560K. ohms R76560K. ohms R94-22K. ohms R84-1OM. ohms R62-varies from one note to another C58--varies from one note to another C128.0039mf.

Cl l2-varies from one note to another C128-.00lmf.

Rl24- 1.2m. ohms R130- 1.2m. ohms Rl40 m. ohms Rl48varies from one note to another Rl54-220K. ohms R160-lm. ohms RIM-680 ohms R174-220K. ohms R176-220l(. ohms R178-220K. ohms C162-25mf.

RIM-3.9K.

R62a-K. ohms R66a-K. ohms R45a-M. ohms R200-5.6K. ohms R94a--K. ohms Rla-K. ohms Rl24a-K. ohms Rl48a-K. ohms C44avaries from one note to another C58a-varies from one note to another Cl06a-varies from one note to another C1l2a-varies from one note to another It will now be seen that the invention as disclosed herein in switching circuits for electronic organs provides a high degree of isolation at a minimum cost of diodes. It also provides for a variable sustain, for special effects such as chimes, and for accompanying wave shaping.

The specific example of the invention herein shown and described will be understood as being for illustrative purposes only. Changes in structure will no doubt occur to those skilled in the art, and will be understood as forming a part of the present invention insofar as they'fall within the spirit and scope of the appended claims.

We claim:

1. A keying system for an electronic musical instrument comprising a plurality of tone generators, each generating electric oscillations corresponding to musical tones, a plurality of first electronic gates, one for each tone generator and respectively connected thereto, each gate normally being off, a junction for each tone generator and each junction connected to a respective electronic gate on the side opposite the respective generator, a plurality of utilization circuits for each tone generator, a plurality of second electronic gates for each tone generator and each connected from said junction to a respective utilization circuit, a first and a second electronic gate therefore being'in series between each generator and a utilization circuit, a plurality of key switch means, and means interconnecting said key switch means and said gates and effective upon operation thereof selectively to open series connected first and second electronic gates whereby selectively to pass electronic oscillations from said generators to said utilization circuits.

2. A keying system as set forth in claim 1 wherein said key switch means comprises a plurality of key switches for each generator, there being at least one key switch for each of said second electronic gates. V

3. A keying system for an electronic musical instrument comprising a plurality of tone generators each generating electrical oscillations corresponding to musical tones, a plurality of first diodes, one for each tone generator and respectively connected thereto, a junction for each tone generator and each junction connected to a respective diode on the side opposite the respective tone generator, a plurality of utilization circuits for each tone generator, a plurality of second diodes for each tone generator and each connected from a respective junction to a respective utilization circuit, all of said diodes normally being biased off, a first and a second diode being in series between each generator and a utilization circuit, a plurality of key switch means, and means interconnecting said key switch means and said diodes and .effective upon operation thereof selectively to bias series connected first and second electronic diodes to conduct and thereby selectively to pass electric oscillations from said generators to said utilization circuits.

4. A keying system for an electronic musical instrument comprising a plurality of tone generators each generating electronic oscillations corresponding to a musical tone and of one polarity relative to ground not exceeding a predetermined potential, a plurality of first diodes, one for each tone generator and respectively connected thereto, each of said first diodes being poled so as not to conduct said electronic oscillations, a junction for each tone generator and each junction being connected to a respective first diode on the side opposite the respective tone generator, a plurality of utilization circuits for each tone generator, a plurality of second diodes for each tone generator and each connected from a respective junction to a respective utilization circuit, said second diodes likewise being poled so as not to conduct said electric oscillations, a first and a second diode being in series between each generator and a utilization circuit, a source of potential of the same polarity as said tone generator oscillations and of greater potential than said predetermined potential, a plurality of key switch means, and means interconnecting said key switch means, said source of potential, and said diodes and effective upon operation of said key switch means selectively to open series connected first and second diodes whereby selectively to pass electric oscillations from said generators to said utilization circuits.

5. A keying system as set forth in claim 4 and further including means to control the buildup and decay of potential of each diode.

6. A keying system as set forth in claim 5 and further including means for varying the rate of at least one of each buildup and decay.

7. A keying system for an electronic musical instrument comprising a plurality of tone generators each generating electrical oscillations corresponding to a musical tone, a plurality of first electronic gates, one for each tone generator and respectively connected thereto, each gate normally being off, a junction for each tone generator, and each junction connected to a respective electronic gate on the side opposite the respective generator, a plurality of utilization circuits for each tone generator, a plurality of second electronic gates for each tone generator and each connectedfrom a respective junction to a respective utilization circuit, a first and a second electronic gate therefore being in series between each generator and a utilization circuit, capacitor means interconnected with said gates and effective upon charging thereof to render said gates conductive, said capacitor means having discharge path means including normally nonconductive diode means, means for selectively rendering said diode means conductive, a plurality of key switch means, and means interconnecting. said key switch means and said gates and capacitor means and effective upon operation thereof selectively to charge said capacitor means and to open series connected first and second electronic gates whereby selectively to pass electric oscillations from said generators to said utilization circuits.

8. A keying system as set forth in claim 7 wherein said discharge path diode means comprises a plurality of diodes, one for each tone generator, and wherein the means for rendering such discharge path diode means conductive comprises a common means for all of said discharge path diodes.

9. A keying system as set forth in claim 7 wherein said discharge path diode means are poled not to conduct, and the means for rendering said discharge path diode means conductive comprises bias means polarized to render said diode means conductive.

10. A keying system as set forth in claim 9 wherein said discharge path diode means comprises a plurality of diodes, there being one such diode for each tone generator, and wherein the means for rendering the diode means conductive comprises a common bias means for simultaneously biasing all of said discharge path diodes for conduction.

H. A keying system as set forth in claim 7 wherein the means for rendering the discharge diode means conductive comprises variable bias means for selectively determining the degree of conduction.

12. A keying system as set forth in claim 11 wherein the discharge path diode means comprises a plurality of diodes, there being one such diode for each I tone generator, and

. wherein the means for rendering said discharge path diodes conductive comprises bias means common to all of said discharge path diodes.

13. A keying system as set forth in claim 11 wherein the discharge path diode means comprises diode means poled normally not to conduct, and wherein the means for rendering said diode means conductive comprises bias means of proper polarity to render said diode means conductive.

14. A keying system as set forth in claim 13 wherein the discharge path diode means comprises a plurality of diodes, there being one such diode for each tone generator, each such diode being poled so as normally not to conduct, and wherein the means for rendering said diode means conductive comprises bias means common to all of the discharge path diodes and poled for rendering said discharge path diodes conductive.

15. A keying system for an electronic musical instrument comprising a plurality of tone generators each generating electric oscillations corresponding to a musical tone, a plurality of first diodes for each tone generator and respectively connected thereto, each of said first diodes normally being nonconductive, a junction for each tone generator and each junction connected to a respective diode on the side opposite the respective generator,a plurality of utilization circuits for each tone generator, a plurality of second diodes for each tone generator and each connected from a respective junction to a respective utilization circuit, all of saidsecond diodes nor mally being nonconductive, a first and a second diode there fore being in series between each generator and a utilization circuit, capacitor means interconnected with said first and second diodes and effective when charged to render said first and second diodes conductive, and discharge path means for said capacitor means including a normally nonconducting electronic gate, and means for selectively rendering said gate conductive, a plurality of key switch means, and means interconnecting said key switch means and said capacitor means and effective upon operation of said key switch means to charge said capacitor means and to render said first and second diodes conductive.

16. A keying system as set forth in claim 15 wherein said electronic gate comprises a plurality of diodes, one for each generator, and wherein said capacitor means comprises a plurality capacitors, one for each generator.

17. A keying system as set forth in claim 16 wherein each gate diode is poled normally not to conduct, and wherein the means for rendering said gate diodes conductive comprises bias means common to all of said gate diodes.

18. A keying system as set forth in claim 15 wherein the means for rendering the gate conductive comprises variable bias means determining the degree of conduction of said gate means.

19. A keying system as set forth in claim 18 wherein the gate comprises a plurality of diodes, there being one such diode for each generator.

20. A keying system for an electronic muscial instrument comprising a plurality of tone generators each generating electric oscillations corresponding to a musical tone, a plurality of electronic gates, one for each tone generator, a plurality of utilization circuits, at least one for each tone generator, said gates respectively interconnecting said generators and said utilization circuits and normally being. off, a plurality of capacitor means respectively interconnecting with said gates and effective when charged to turn said gates on, discharge path means for said capacitor means and including a plurality of discharge electronic gates bias means for controlling the conductivity of said discharge electronic gates, a plurality of key switch means, and means interconnecting said key switch means and said capacitor means and effective upon operation of said key switch means selectively to charge said capacitors to render said first mentioned electronic gates conductive whereby selectively to pass electric oscillations from said tone generators to said utilization circuits.

21. A keying system as set forth in claim 20 wherein the discharge gates comprise a plurality of diodes, one for each generator, and wherein the means for controlling conduction of said discharge gates comprises common bias means interconnected with each of said discharge gate diodes.

22. A keying system as set forth in claim 21 including variable bias means whereby to vary the conductivity of discharge gate diodes in common.

23. A keying system for a electronic musical instrument comprising a plurality of tone generators each generating electric oscillations corresponding to a musical tone, a plurality of first electronic gates, one for each tone generator and respectively connected thereto, each gate normally being off, a first junction for each tone generator and each first junction connected to a respective electronic gate on the side opposite the respective generator, a plurality of utilization circuits for each tone generator, a plurality of second electronic gates for each tone generator and each coimected from a respective first junction to a respective utilization circuit, a first and a second electronic gate therefore being in series between each generator and a utilization circuit, a plurality of second junctions respectively connected to certain of said second electronic gates on the side opposite the first junction, a plurality of normally off additional electronic gates connected in groups to said second junctions, and said additional gates further being connected each to a different predetermined tone generator, a plurality of key switch means for selectively turning on first and second series connected diodes to play musical note, and additional key switch means for turning on said additional electronic gates, turning on of said additional gates producing simultaneous playing of a plurality of notes and simulating a chimes effect.

24. A keying system as set forth in claim 23 wherein the additional key switch means co prises a plurality of key switches each controlled by a different key and each connected to a different group of said additional electronic gates, each of the gates of a group being connected to a difierent second junction.

25. A keying system as set forth in claim 24 wherein each electronic gate comprises a diode normally nonconducting.

26. A keying system for an electronic musical instrument comprising a plurality of tone generators each generating electric oscillations corresponding to musical tones comprising the gamut of said instrument, a plurality'of first electronic gates, each gate normally being off, a plurality of utilization circuits, said first electronic gates respectively interconnecting said tone generators and said utilization circuits, a plurality of groups of additional electronic gates, each group of additional electronic gates being connected respectively to predetermined ones of said first electronicgates, said additional electronic gates normally being off, a plurality of key switch means, and means respectively interconnecting said key switch means and said gates and effective upon operation of said key switch means selectively to open the first electronic gates to play musical tones and effective to open the additional electronic gates and thereby to open said first electronic gates in predetermined groups to provide a combination of tones simulating a chimes effect.

27. A keying system as set forth in claim 26 wherein each of said electronic gates comprises a diode.

28. A keying system for an electronic musical instrument comprising a plurality of tone generators each generating elec tric oscillations corresponding to a musical tone, the frequency of each generator being different in accordance with the gamut of the instrument and the oscillations generated comprising square wave oscillations always of one polarity, a plurality of electronic gates respectively connected to said tone generators, utilization circuit means connected to said electronic gates, said gates normally being off and effective when on to transmit electric oscillations'to said utilization circuit means, a source of electric potential of said polarity, key switch means interconnected with said electronic gates and with said source of electric potential for selectively opening said gates upon operation of said key switch means, and integrating means associated with each gate and effective to round off the input of said square wave electric oscillations, said integrating means comprising a plurality of shunting capacitors respectively on the side of each gate opposite the respective generator, and a plurality of resistors respectively connected from said key switches to said gates on the side of said gates opposite said tone generators, the oscillations passed by said gates to said utilization circuit means therefore changing from a square wave toward a saw tooth wave supplied with potential through circuits which serve as integrating circuits for the square waves, whereby to round off the attack to produce or lead toward saw tooth wave shapes. Groups of diodes also are provided with are switched on simultaneously, and are connected to the previously mentioned diodes for playing preselected groups of notes simultaneously to simulate a chimes effect.

29. A keying system as set forth in claim 28 wherein each electronic gate comprises a diode.

30. A keying system for an electronic musical instrument comprising a plurality of tone generators each generating electric oscillation corresponding to a musical tone, the oscillations of each generator being of a different frequency in accordance with the gamut of the instrument, and each electric oscillation comprising a square wave, a plurality of first electronic gates, one for each tone generator and respectively connected thereto, each gate normally being off, a junction for each tone generator and each junction connected to a respective electronic gate on the side opposite the respective generator, a plurality of utilization circuits for each tone generator, a plurality of second electronic gates for each tone generator and each connected from a respective junction to a respective utilization circuit, a first and a second electronic gate therefore being in series between each generator and a utilization circuit, a plurality of key switch means, means connecting said key switch means and said gates and effective upon operation thereof selectively to open series honnected first and second electronic gates whereby selectively to pass electric oscillations from said generators to said utilization circuits, and a plurality of means respectively associated with each of said gates for rounding off being constant from one gate to another and hence of greater effect with increasing frequency, the oscillations as passed by the second electronic gates therefore being substantially square wave oscillations at low frequency and progressively approaching a saw tooth wave with increasing frequency.

31. A keying system as set forti in claim 30 wherein each electronic gate comprises a diode.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 ,569,604

Dated March 9, 1971 Inventor-(s) Harold 0. Schwartz, William V. Machanian and Richard E. Barbas It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1, line Column 3 line Column 3 line Column 4, line Column 7, line Column change "in" to --is-- change 'through n" to --through l48-n change "is" to --in-- after "positive" cancel --v--. through Column 8, line 2, see attache listing.

10, line 67 change "a electronic" to --an electr Column 12, lines 15-21, place a period after "wave" and cancel --supplied with potential through circuits which as integrating circuits for the square waves whereby to off the attack to produce or lead toward saw tooth wave Groups of diodes also are provided with are switched on taneously, and are connected to the previously mentioned diodes for playing preselected groups of notes simultane to simulate a chimes effect" UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,569,604 Dated March 9, 1971 Inventor(s) Harold O. Schwartz, William V. Machanian and Richard E Barbas It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 7 line 57 through Column 8, line 2 should reac as follows:

R62a 220K. ohms R66a 220K. ohms R78 270K. ohms R4561 lM. ohms R76a 3.9K. ohms R200 5.6K. ohms R94a 470K. ohms Rll6a 220K. ohms Rl20a 220K. ohms Rl24a 270K. ohms Rl +0a 470K. ohms Rl30a 3.9K. ohms R212 5.6K. ohms Rl48a 470K. ohms C38a 470 pf. C44a varies from one note to another C58a varies from one note to another 090a 2.2mf. Cl06a varies from one note to another Cll2a varies from one note to another 0142a 2.2mf.

Signed and sealed this 16th day of November 1971 (SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Acting Commissioner of Pat 

1. A keying system for an electronic musical instrument comprising a plurality of tone generators, each generating electric oscillations corresponding to musical tones, a plurality of first electronic gates, one for each tone generator and respectively connected thereto, each gate normally being off, a junction for each tone generator and each junction connected to a respective electronic gate on the side opposite the respective generator, a plurality of utilization circuits for each tone generator, a plurality of second electronic gates for each tone generator and each connected from said junction to a respective utilization circuit, a first and a second electronic gate therefOre being in series between each generator and a utilization circuit, a plurality of key switch means, and means interconnecting said key switch means and said gates and effective upon operation thereof selectively to open series connected first and second electronic gates whereby selectively to pass electronic oscillations from said generators to said utilization circuits.
 2. A keying system as set forth in claim 1 wherein said key switch means comprises a plurality of key switches for each generator, there being at least one key switch for each of said second electronic gates.
 3. A keying system for an electronic musical instrument comprising a plurality of tone generators each generating electrical oscillations corresponding to musical tones, a plurality of first diodes, one for each tone generator and respectively connected thereto, a junction for each tone generator and each junction connected to a respective diode on the side opposite the respective tone generator, a plurality of utilization circuits for each tone generator, a plurality of second diodes for each tone generator and each connected from a respective junction to a respective utilization circuit, all of said diodes normally being biased off, a first and a second diode being in series between each generator and a utilization circuit, a plurality of key switch means, and means interconnecting said key switch means and said diodes and effective upon operation thereof selectively to bias series connected first and second electronic diodes to conduct and thereby selectively to pass electric oscillations from said generators to said utilization circuits.
 4. A keying system for an electronic musical instrument comprising a plurality of tone generators each generating electronic oscillations corresponding to a musical tone and of one polarity relative to ground not exceeding a predetermined potential, a plurality of first diodes, one for each tone generator and respectively connected thereto, each of said first diodes being poled so as not to conduct said electronic oscillations, a junction for each tone generator and each junction being connected to a respective first diode on the side opposite the respective tone generator, a plurality of utilization circuits for each tone generator, a plurality of second diodes for each tone generator and each connected from a respective junction to a respective utilization circuit, said second diodes likewise being poled so as not to conduct said electric oscillations, a first and a second diode being in series between each generator and a utilization circuit, a source of potential of the same polarity as said tone generator oscillations and of greater potential than said predetermined potential, a plurality of key switch means, and means interconnecting said key switch means, said source of potential, and said diodes and effective upon operation of said key switch means selectively to open series connected first and second diodes whereby selectively to pass electric oscillations from said generators to said utilization circuits.
 5. A keying system as set forth in claim 4 and further including means to control the buildup and decay of potential of each diode.
 6. A keying system as set forth in claim 5 and further including means for varying the rate of at least one of each buildup and decay.
 7. A keying system for an electronic musical instrument comprising a plurality of tone generators each generating electrical oscillations corresponding to a musical tone, a plurality of first electronic gates, one for each tone generator and respectively connected thereto, each gate normally being off, a junction for each tone generator, and each junction connected to a respective electronic gate on the side opposite the respective generator, a plurality of utilization circuits for each tone generator, a plurality of second electronic gates for each tone generator and each connected from a respective junction to a respective utilization circuit, a first and a second electronic gate therefore being in series between each generator and a utilization circuit, capacitor means interconnected with said gates and effective upon charging thereof to render said gates conductive, said capacitor means having discharge path means including normally nonconductive diode means, means for selectively rendering said diode means conductive, a plurality of key switch means, and means interconnecting said key switch means and said gates and capacitor means and effective upon operation thereof selectively to charge said capacitor means and to open series connected first and second electronic gates whereby selectively to pass electric oscillations from said generators to said utilization circuits.
 8. A keying system as set forth in claim 7 wherein said discharge path diode means comprises a plurality of diodes, one for each tone generator, and wherein the means for rendering such discharge path diode means conductive comprises a common means for all of said discharge path diodes.
 9. A keying system as set forth in claim 7 wherein said discharge path diode means are poled not to conduct, and the means for rendering said discharge path diode means conductive comprises bias means polarized to render said diode means conductive.
 10. A keying system as set forth in claim 9 wherein said discharge path diode means comprises a plurality of diodes, there being one such diode for each tone generator, and wherein the means for rendering the diode means conductive comprises a common bias means for simultaneously biasing all of said discharge path diodes for conduction.
 11. A keying system as set forth in claim 7 wherein the means for rendering the discharge diode means conductive comprises variable bias means for selectively determining the degree of conduction.
 12. A keying system as set forth in claim 11 wherein the discharge path diode means comprises a plurality of diodes, there being one such diode for each tone generator, and wherein the means for rendering said discharge path diodes conductive comprises bias means common to all of said discharge path diodes.
 13. A keying system as set forth in claim 11 wherein the discharge path diode means comprises diode means poled normally not to conduct, and wherein the means for rendering said diode means conductive comprises bias means of proper polarity to render said diode means conductive.
 14. A keying system as set forth in claim 13 wherein the discharge path diode means comprises a plurality of diodes, there being one such diode for each tone generator, each such diode being poled so as normally not to conduct, and wherein the means for rendering said diode means conductive comprises bias means common to all of the discharge path diodes and poled for rendering said discharge path diodes conductive.
 15. A keying system for an electronic musical instrument comprising a plurality of tone generators each generating electric oscillations corresponding to a musical tone, a plurality of first diodes for each tone generator and respectively connected thereto, each of said first diodes normally being nonconductive, a junction for each tone generator and each junction connected to a respective diode on the side opposite the respective generator, a plurality of utilization circuits for each tone generator, a plurality of second diodes for each tone generator and each connected from a respective junction to a respective utilization circuit, all of said second diodes normally being nonconductive, a first and a second diode therefore being in series between each generator and a utilization circuit, capacitor means interconnected with said first and second diodes and effective when charged to render said first and second diodes conductive, and discharge path means for said capacitor means including a normally nonconducting electronic gate, and means for selectively rendering said gate conductive, a plurality of key switch means, and means interconnecting said key switch means and said capacitor means and effective upon operation of said key switch means to charge said capacitor means and to render said first and second diodes conductive.
 16. A keying system as set forth in claim 15 wherein said electronic gate comprises a plurality of diodes, one for each generator, and wherein said capacitor means comprises a plurality capacitors, one for each generator.
 17. A keying system as set forth in claim 16 wherein each gate diode is poled normally not to conduct, and wherein the means for rendering said gate diodes conductive comprises bias means common to all of said gate diodes.
 18. A keying system as set forth in claim 15 wherein the means for rendering the gate conductive comprises variable bias means determining the degree of conduction of said gate means.
 19. A keying system as set forth in claim 18 wherein the gate comprises a plurality of diodes, there being one such diode for each generator.
 20. A keying system for an electronic muscial instrument comprising a plurality of tone generators each generating electric oscillations corresponding to a musical tone, a plurality of electronic gates, one for each tone generator, a plurality of utilization circuits, at least one for each tone generator, said gates respectively interconnecting said generators and said utilization circuits and normally being off, a plurality of capacitor means respectively interconnecting with said gates and effective when charged to turn said gates on, discharge path means for said capacitor means and including a plurality of discharge electronic gates bias means for controlling the conductivity of said discharge electronic gates, a plurality of key switch means, and means interconnecting said key switch means and said capacitor means and effective upon operation of said key switch means selectively to charge said capacitors to render said first mentioned electronic gates conductive whereby selectively to pass electric oscillations from said tone generators to said utilization circuits.
 21. A keying system as set forth in claim 20 wherein the discharge gates comprise a plurality of diodes, one for each generator, and wherein the means for controlling conduction of said discharge gates comprises common bias means interconnected with each of said discharge gate diodes.
 22. A keying system as set forth in claim 21 including variable bias means whereby to vary the conductivity of discharge gate diodes in common.
 23. A keying system for a electronic musical instrument comprising a plurality of tone generators each generating electric oscillations corresponding to a musical tone, a plurality of first electronic gates, one for each tone generator and respectively connected thereto, each gate normally being off, a first junction for each tone generator and each first junction connected to a respective electronic gate on the side opposite the respective generator, a plurality of utilization circuits for each tone generator, a plurality of second electronic gates for each tone generator and each connected from a respective first junction to a respective utilization circuit, a first and a second electronic gate therefore being in series between each generator and a utilization circuit, a plurality of second junctions respectively connected to certain of said second electronic gates on the side opposite the first junction, a plurality of normally off additional electronic gates connected in groups to said second junctions, and said additional gates further being connected each to a different predetermined tone generator, a plurality of key switch means for selectively turning on first and second series connected diodes to play musical note, and additional key switch means for turning on said additional electronic gates, turning on of said additional gates producing simultaneous playing of a plurality of notes and simulating a chimes effect.
 24. A keying system as set forth in claim 23 wherein the additional key switch means comprises a plurality of key sWitches each controlled by a different key and each connected to a different group of said additional electronic gates, each of the gates of a group being connected to a different second junction.
 25. A keying system as set forth in claim 24 wherein each electronic gate comprises a diode normally nonconducting.
 26. A keying system for an electronic musical instrument comprising a plurality of tone generators each generating electric oscillations corresponding to musical tones comprising the gamut of said instrument, a plurality of first electronic gates, each gate normally being off, a plurality of utilization circuits, said first electronic gates respectively interconnecting said tone generators and said utilization circuits, a plurality of groups of additional electronic gates, each group of additional electronic gates being connected respectively to predetermined ones of said first electronic gates, said additional electronic gates normally being off, a plurality of key switch means, and means respectively interconnecting said key switch means and said gates and effective upon operation of said key switch means selectively to open the first electronic gates to play musical tones and effective to open the additional electronic gates and thereby to open said first electronic gates in predetermined groups to provide a combination of tones simulating a chimes effect.
 27. A keying system as set forth in claim 26 wherein each of said electronic gates comprises a diode.
 28. A keying system for an electronic musical instrument comprising a plurality of tone generators each generating electric oscillations corresponding to a musical tone, the frequency of each generator being different in accordance with the gamut of the instrument and the oscillations generated comprising square wave oscillations always of one polarity, a plurality of electronic gates respectively connected to said tone generators, utilization circuit means connected to said electronic gates, said gates normally being off and effective when on to transmit electric oscillations to said utilization circuit means, a source of electric potential of said polarity, key switch means interconnected with said electronic gates and with said source of electric potential for selectively opening said gates upon operation of said key switch means, and integrating means associated with each gate and effective to round off the input of said square wave electric oscillations, said integrating means comprising a plurality of shunting capacitors respectively on the side of each gate opposite the respective generator, and a plurality of resistors respectively connected from said key switches to said gates on the side of said gates opposite said tone generators, the oscillations passed by said gates to said utilization circuit means therefore changing from a square wave toward a saw tooth wave supplied with potential through circuits which serve as integrating circuits for the square waves, whereby to round off the attack to produce or lead toward saw tooth wave shapes. Groups of diodes also are provided with are switched on simultaneously, and are connected to the previously mentioned diodes for playing preselected groups of notes simultaneously to simulate a chimes effect.
 29. A keying system as set forth in claim 28 wherein each electronic gate comprises a diode.
 30. A keying system for an electronic musical instrument comprising a plurality of tone generators each generating electric oscillation corresponding to a musical tone, the oscillations of each generator being of a different frequency in accordance with the gamut of the instrument, and each electric oscillation comprising a square wave, a plurality of first electronic gates, one for each tone generator and respectively connected thereto, each gate normally being off, a junction for each tone generator and each junction connected to a respective electronic gate on the side opposite the respective generator, a plurality of utilization circuIts for each tone generator, a plurality of second electronic gates for each tone generator and each connected from a respective junction to a respective utilization circuit, a first and a second electronic gate therefore being in series between each generator and a utilization circuit, a plurality of key switch means, means connecting said key switch means and said gates and effective upon operation thereof selectively to open series connected first and second electronic gates whereby selectively to pass electric oscillations from said generators to said utilization circuits, and a plurality of means respectively associated with each of said gates for rounding off being constant from one gate to another and hence of greater effect with increasing frequency, the oscillations as passed by the second electronic gates therefore being substantially square wave oscillations at low frequency and progressively approaching a saw tooth wave with increasing frequency.
 31. A keying system as set forth in claim 30 wherein each electronic gate comprises a diode. 